Cohesion between grains in a geological system is perhaps the simplest and ideal representation of a range of material systems including soft rocks, structured soils, mudstones, cemented sands, powder compacts, and carbonate sands. This presence of inter granular cohesion is known to alter the ensemble mechanical response when subjected to varied boundary conditions. In this study, a hollow cylinder apparatus is used to investigate the mechanical behavior of weakly cemented sand ensembles by mapping the state boundary surfaces including the failure surface (locus of peak stress state) and the state of plastic flow (locus of final stress state). When these materials are sheared, the plastic deformation accumulates due to breakdown of cohesion between the grains, which introduces a lag in occurrence of peak stress ratio and maximum dilatancy, unlike a typical frictional granular material. This breakdown of cementation is affected by changes in the initial mean effective stress, initial reconstitution density, and intermediate principal stress ratio (stress path on the octahedral plane). The final state locus, emergent at large strains, was found to depend on the initial reconstitution density. Further, the parameters are extracted for calibration and prediction exercise using an elastic plastic constitutive model. In this and several other models, the effect of cementation is considered as an additional confinement to the ensemble. Such an approach predicts the stress state precisely but does not predict the volumetric response accurately, especially at large strains. © 2021 American Society of Civil Engineers.